3 Executive Summary This ABI Cloud Height Algorithm (ACHA) generates the Option 1 products of Cloud-top Height, Temperature, Pressure and Cloud Layers. Version 5 was delivered in May. ATBD (100%) is on track for a July delivery A unique 3-channel IR-only approach has been developed that utilizes improved ABI spectral capabilities over GOES-IM and GOES-NOP. CALIPSO validation tools have been developed and applied to 10 weeks of SEVIRI data. CALIPSO analysis indicates spec compliance for all products. 3

4 Algorithm Summary We developed an algorithm that uses the 11, 12 and 13.3 μm observations to give us the ability to estimate cloud height and cloud microphysics. The algorithm uses an optimal estimation approach that provides error estimates. We use state-of-the-art scattering calculations to model the variation of cloud emissivity between 11, 12 and 13.3 μm. For multi-layer clouds, we estimate the lower cloud height from surrounding pixels. Cloud emissivity (11 μm) and a microphysical index (β 11&12 μm) are also generated automatically in the retrieval. Cloud layer is retrieved using the cloud-top pressure and the assumed pressure boundaries for High, Mid and Low clouds. Cloud heights in the presence of low level inversions are handled using the similar logic that is employed in the MODIS algorithms. 4

5 Motivation for ACHA Channel Selection The following figures illustrate the impact of the spectral information on how sensitive an algorithm is to the cloud-top pressure. Grey regions indicate the regions where a cloud could exist and match the observations used in algorithm. 532 nm CALIPSO backscatter. GOES-R ABI ACHA MODIS IR False Color + CALIPSO Track. NPOESS-VIIRS (aka GOES-IM) 5

6 Example ACHA Output Images below show an example of the information provided by the ACHA for severe convection case in July 2007 over Poland seen by Meteosat μm Brightness Temperature (K) Cloud-top Pressure (hpa) 6

8 Example ACHA Output In addition to the Option 1 Cloud Height, Temperature and Pressure products, the ACHA makes cloud emissivity and microphysics (particle size). These products are required for accurate cloud heights. They are also of value especially in the terminator where the day and night cloud microphysical properties are challenged. 11 μm Brightness Temperature (K) Cloud Emissivity (11 μm) 8

11 Qualifiers Theses are made with the following qualifiers. Sensor zenith angle < 65 degrees Cloud mask and cloud type available 11

12 Validation Approach With the launch of CALIPSO/CloudSat in 2006, NASA now provides information on the vertical profile of cloud and aerosol. With high sensitivity to the presence of cloud, the CALIPSO data have been used as our primary ACHA validation tool. We have co-located CALIPSO with SEVIRI for the 10-week analysis period and this serves as our primary validation dataset. Comparisons with MODIS, which offers heights from a CO 2 slicing technique, are also valuable for algorithm validation. 12

13 Validation Approach For every cloudy CALIPSO pixel, the CALIPSO 1km Cloud Layer product provides information on the top and base of up to 10 cloud layers. The mean temperature of the layers are also provided. Using the knowledge of the clear-sky radiative transfer that we use for the algorithm and the observed 11 μm radiance, we can take the cloud heights from CALIPSO and estimate cloud emissivities. Therefore we can bin the ACHA performance by both cloud height and cloud emissivity (the two main drivers of performance). This is illustrated below. X 20 Z c X 0 e c

15 MODIS Cloud Pressure Validation MYD06 provides cloud height using a CO 2 slicing approach that has been well-characterized. The image on the right shows a comparison of the ACH run on SEVIRI compared to MODIS results for simultaneously observed pixels. Accuracy = -24 hpa Precision = 80 hpa These stats are computed for all pixels - not just thick low clouds. 15

17 Summary The ABI Cloud Height Algorithm provides a unique IR-only solution that utilizes the new capabilities offered by the ABI Version 5 is delivered and the 100% ATBD is coming. These products meet the specifications and are proving useful to downstream applications (AMV) 17

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